Our multifaceted investigation on normal and atypical melanocytes concerns the following topics: 1. Characterization of the receptors for MSH on melanoma cells. 2. Studies on the action of interferon on melanoma cells. 3. A study of regulatory points in melanin biosynthesis. 4. The cytotoxicity of substances produced by the tyrosine-tyrosinase reaction. 5. The mechanism of internalization of the MSH-receptor complex. 6. The mechanism by which cAMP increases the activity of tyrosinase. 7. The culturing of normal melanocytes.